Axial magnetic bearing apparatus

Abstract

In axial magnetic bearing apparatus in which a rotary disc made of a magnetic material is fixedly attached to a rotating shaft, and electromagnets are disposed on opposite sides of the rotary disc so as to have suitable very small distances therefrom respectively, so as to bear the rotating shaft axially in a non-contact state, a deep groove for forming an air layer having large magneto-resistance is provided all over the outer circumference of the rotary disc. Thus, formation of a magnetic circuit not contributing to position control is relieved, and the weight of the disc is reduced so that the position control performance of the axial magnetic bearing and the natural frequency of a rotor are improved.

1. Axial magnetic bearing apparatus comprising:
 a casing; 
 a rotating shaft; 
 a rotary disc made of a magnetic material which is fixedly attached to the rotating shaft, said rotary disc having a groove which extends in a radial direction of the disc such that an air layer having magneto resistance is provided in the groove, said groove only opening to an outer radial circumference of the rotary disk; 
 a pair of electromagnetic stators which are fixed to the casing and located on opposite sides of said rotary disc, each of the stators having a coil slot; 
 ring-like electromagnetic coils which generate magnetomotive force, said electromagnetic coils being respectively inserted into the coil slots, 
 wherein on the basis of an output signal of a displacement sensor for measuring axial displacement of said rotating shaft, magnetic attraction force is made to act between said rotary disc and each of said electromagnetic stators so as to bear said rotating shaft in a target position distant from said electromagnetic stators and in non-contact therewith. 
 
   
   
     2. The axial magnetic bearing apparatus of  claim 1 , wherein the electromagnetic stators comprise magnet pole teeth, and wherein outer circumferential grooves which form an air layer having magneto-resistance are provided respectively in outer radial portions of the magnet pole teeth not opposed to said rotary disc, so as to extend axially from a side where said rotary disc is located. 
   
   
     3. The axial magnetic bearing apparatus of  claim 1 , wherein said groove is formed in an axial center of the rotary disc. 
   
   
     4. The axial magnetic bearing apparatus of  claim 1 , wherein said groove extends from the outer radial circumference of the rotary disc towards the rotating shaft. 
   
   
     5. The axial magnetic bearing apparatus of  claim 1 , wherein said groove is positioned between the coils. 
   
   
     6. The axial magnetic bearing apparatus of  claim 1 , wherein a first magnetic circuit is formed between one of said stators and said rotary disk and a second magnetic circuit is formed between the other of said stators and said rotary disk, the first and second magnetic circuits being separated by said groove such that said first and second magnetic circuits are insulated from each other magnetically. 
   
   
     7. The axial magnetic bearing apparatus of  claim 1 , further comprising a first outer circumferential groove and a second outer circumferential groove, said first outer circumferential groove being positioned above one said coils in the radial direction and said second outer circumferential groove being positioned above the other coil in the radial direction, such that an air layer is formed extending from said first outer circumferential groove to said second outer circumferential groove. 
   
   
     8. The axial magnetic bearing apparatus of  claim 1 , wherein said stators respectively include a circumferential groove extending axially in opposite directions away from the rotary disk.